Many would think that free diving is an inferior form of diving
compared to SCUBA diving, after all, what can a free diver do that
a SCUBA diver can't? Actually, quiet a lot, a free diver can dive unencumbered,
any time, time after time, and experience being underwater in a more natural
manner. As a SCUBA diver myself, I can't say I particularly enjoy the
experience, but many find it great.

Technique

Everyone who has held their breath knows that after a short period
of time, your lungs begin to feel like they are on fire. This is
not caused by the lack of oxygen, but the build up of carbon dioxide.
Generally when you experience this sensation you still have plenty of
oxygen in your lungs, which is were hyperventilating comes in.
By hyperventilating you purge your lungs of most of the carbon dioxide that
is always in them. Thus allowing you to fill your lungs with more oxygen
and preventing the breath reflex from coming in too soon.

Variable ballast

Limited refers to the diver using one a guided ballast device for the
decent. The diver may use a propulsion device (eg fins).

Unlimited refers to the diver using a guided ballast device for the
decent and a guided flotation device for the accent.

Dangers

I won't even begin to go into the numerous dangers there are with
free-diving. If you attempt to override your bodies natural defences
against suffocating by hyperventilating or using other special techniques,
you run into dangers. Much like with SCUBA diving, you should consult
a trained professional before attempting free diving.

Records

These change over time, and by the time you read this, these are
probably wrong.